Towards the beginning of the movie, Brad and Janet are approaching
the mansion in a rainstorm, and a pennon can be seen flying from the
mansion's roof.

Sadly, my copy of the video is getting very worn, but I think the
design is a white pennon with a black circle, on which is a white
lightning bolt. A similar emblem appears one Riff-Raff's costume
towards the end of the movie.

Presumably, this is the flag of the planet Transsexual, in the galaxy
of Transylvania (not to be confused with the central European region
or Transylvania!)
James Dignan, 27 May 2004